Real Dictionary

biofeedback in American English
a technique of seeking to control certain emotional states, such as anxiety or depression, by training oneself, with the aid of electronic devices, to modify autonomic body functions, such as blood pressure or heartbeat
noun: a method of learning to control one's bodily functions by monitoring one's own brain waves, blood pressure, degree of muscle tension, etc

biofeedback in British English
noun: a technique for teaching the control of autonomic functions, such as the rate of heartbeat or breathing, by recording the activity and presenting it (usually visually) so that the person can know the state of the autonomic function he or she is learning t